The invention relates to an industrial furnace having a tubular burner, in accordance with the preamble to claim 1.
A particularly preferred field of application for such an industrial furnace is in installations for the heat treatment of mineral goods, for example, furnaces or furnace systems for the heat treatment or calcining of cement clinker, lime, ores and so on; industrial furnaces and industrial furnace systems that come into consideration are in particular rotary tubular kilns, calcining furnaces and calcining installations etc.
It is exactly with industrial furnaces of the above-mentioned kind that it is important that the process of combustion can be influenced by the configuration and mode of operation of the burner, in order to be able to carry out the industrial processes in such industrial furnaces or furnace systems, for example, to be in with the particular properties of the raw material, the desired quality features of the product to be produced, different types of fuel and so on. Furthermore, at the same time the stipulated emission values of such industrial furnaces, for instance in respect of carbon dioxide and nitrogen oxide, must also be adhered to, wherein it is desirable for the associated burner, and hence also the corresponding furnace, to be operated in an energy-efficient and cost-effective manner. To that end, efforts have been made to develop an optimum flame in the furnace combustion zone by means of the burner, by effecting favourable mixing of the incoming combustion air or the incoming combustion gas with the incoming fuel.
Different burner constructions are therefore already known (e.g. DE-A-43 19 363 and DE-A-196 48 981), in which several coaxially arranged tube walls define several separate feed ducts of approximately annular cross-section for combustion gas or combustion air and fuel. In this connection, at the burner front end of the outer annular feed duct intended for the supply of combustion gas, the end discharging into the combustion zone, there are arranged individual nozzles in approximately annular distribution, which surround a fuel feed duct lying within this combustion gas feed duct and are intended to ensure that the incoming fuel and the combustion gas are mixed in that they are adjustable in respect of their radial and/or tangential discharge direction. Practical operation has shown that the desired good mixing between combustion gas or combustion air and fuel can be achieved only to a very unsatisfactory degree. In this connection, above all the secondary combustion air (secondary air) introduced separately into the combustion zone and flowing towards it in the outer circumferential region of the burner is usually insufficiently incorporated into this mixture of combustion gas/combustion air and fuel.
The prior patent application EP-A-0 974 552 relates to a burner for partial oxidation of hydrogen sulphide for the formation of sulphur vapour. The burner comprises a plurality of tube walls arranged radially spaced with respect to one another and coaxially one inside the other, which bound a plurality of separate feed ducts of approximately annular cross-section for combustion gas and fuel with hydrogen sulphide. The outermost annular feed duct is provided for fuel containing hydrogen sulphide. The discharge region of the burner is arranged in an orifice of the combustion zone, a further annular duct for supply of combustion air being formed by the discharge region of the burner and the orifice of the combustion zone.
The invention is therefore based on the problem of so improving an industrial furnace having a burner in accordance with the preamble to claim 1 that the incorporation of fuel into the combustion gas as a whole or into the combustion air as a whole, and hence the entire process of combustion (ignition, thorough combustion of the fuels, NOx evolution, flame form and length), can be optimally influenced.
That problem is solved in accordance with the invention by the characterising clause of claim 1.
Advantageous constructions of the invention are specified in the subsidiary claims.
Looking at the cross-section of the inner burner mouthpiece, in the case of the industrial furnace according to the invention having a tubular burner the outermost annular feed duct is in the form essentially of a fuel feed duct, and the combustion gas feed duct equipped with the individual nozzles is arranged radially within this fuel feed duct. If this construction in accordance with the invention is applied, for example, to a use of this burner that is especially representative of actual service, for instance in a rotary tubular kiln, into the combustion zone of which oxygen-rich, pre-warmed secondary combustion air, so-called xe2x80x9csecondary air, is supplied directly, for example, from a cooler downstream of the rotary tubular kiln, in which process it flows at least partially along or towards the outer circumferential side of the inner burner end section, whilst further combustion gas, especially so-called xe2x80x9cprimary airxe2x80x9d is fed via the inner ring of individual nozzles and fuel is fed through the outer annular fuel feed duct, it can readily be appreciated that the fuel flowing into the combustion zone is blown positively through the radially inner individual nozzles by means of the primary air into the secondary combustion air flowing in from the outside. This means, therefore, that the primary air (as combustion gas) flowing in. via the individual nozzles blows the fuel flowing in through the at least one outer fuel feed duct at least approximately radially outwards towards the circumference of the burner, and hence into the incoming secondary air there, with the result that a very intensive and rapid mixing . . . [of primary air and fuel into the secondary air flowing in from the outside takes place.] furnaces or calciners, in furnaces for the calcining of lime, for the heat treatment of ores and suchlike.
In respect of their discharge direction, the individual nozzles can be oriented not only parallel, but also at a specific angle to the discharge direction of the fuel feed duct externally surrounding them. In this connection, it is also conceivable for the alignment angle of the individual nozzles to be adjustable. If the individual nozzles are oriented obliquely with respect to the discharge direction of the fuel feed duct surrounding them, it is possible for the primary air (or primary combustion gas) flowing into the combustion zone via the individual nozzles to be blown so that it diverges outwardly to a greater or lesser extent. With a skewed arrangement of the individual nozzles with respect to the fuel feed duct surrounding them, a corresponding swirl can additionally be generated, so that the mixing effect of primary air and fuel with the secondary air, and hence the influencing of the entire process of combustion, can be correspondingly intensified. In accordance with the one structural alternative and based on optimum findings, this orientation of the individual nozzles can therefore be fixed as a basic setting, or, in accordance with the other structural alternative, the individual nozzles can be re-set time and again depending on the particular conditions (either during operation, or during a stoppage).
At this point, it should be pointed out that although the at least one outer fuel feed duct is intended essentially for feed of the appropriate fuels (liquid or gaseous or fine-grained or in powder form), it is quite possible for a certain proportion of combustion air (in admixture with the fuels) to be fed in through the fuel feed duct. Similarly, as required, a certain proportion of fuel can be intermixed with the combustion gas fed in via the individual nozzles or with the primary air introduced there.